The commercially available electroplating processes and baths for producing white gold alloys are based on cyanide-containing electroplating baths. However, such baths are notoriously unstable with respect to color and deposit composition.
Also, the known electroplating processes for obtaining pink gold alloys generally use an acidic gold cyanide-containing electroplating baths as described in British No. 1,224,507. However, such pink gold alloys are usually difficult to obtain because the presence of copper, which is the main alloying metal producing the pink coloration, makes the bath sensitive to operating parameters, especially changes in concentration. Uniformly reproducable, hard, bright gold-copper alloys having a pink coloration can normally be obtained from such acid cyanide baths only by careful regulation of the bath components and operating conditions.
Another difficulty is the necessity of removing from the spent baths any remaining cyanide so as to provide a cyanide-free effluent which will not give rise to pollution problems.
Recently there has been disclosed an electroplating bath for producing a pink gold-alloy deposit which utilizes an amino-gold sulphite complex. The said complex is formed by reacting a trivalent gold compound with an amine followed by the reaction of the resulting product with an alkali metal or ammonium sulphite in at least twice the molar quantity. This process is described in British No. 1,325,352. However, in practice, this bath is not easy to operate and it is relatively expensive. Also, it has the disadvantages of becoming easily poisoned by airborne or dragged-in cyanide contamination which gives rise to color stability problems.